if i replace my ignition cylinder and housing do i need a need pcm for my car to start

Hi, my name is Devin. I am an auto repair expert with the Car Genius team here at RepairPal. I'm sorry to hear you're having trouble with your Tahoe. If you've replaced the ignition cylinder and housing, it's likely that your vehicle's anti-theft system (Passlock) is preventing it from starting because the new key and ignition cylinder may not be recognized. Typically, you won't need to replace the PCM (Powertrain Control Module), but you will need to reprogram or relearn the Passlock system to allow the vehicle to start with the new ignition setup. This can sometimes be done by performing a key relearn procedure, which involves leaving the key in the "ON" position for about 10 minutes (or until the security light goes off) and repeating this process three times. If that doesn't work, you may need a locksmith or dealership to reprogram it properly. If you need more advice, have any other questions about your vehicle, or would like to get connected to a RepairPal Certified shop near you, we have you covered. Give us a call at 877-913-1554, and we will happily help you out!